The presence of mucous secretions with abnormal viscoelastic properties of the tracheobronchial tree is the most widely known feature of patients with cystic fibrosis (CF). This results in the obstruction of the lung airways and leads to chronic pulmonary disease which is responsible for most of the mortality in CF patients. The objectives of this research proposal are to investigate the basis of altered viscoelastic properties of the CF secretions. The specific objectives are a) to determine if the altered viscoelastic properties of CF tracheobronchial secretions correlate with changes in the biochemical composition (e.g., increased level of sulfation of CF mucin as compared to normal mucin) or with changes in biophysical properties of mucin molecules (e.g., molecular aggregation characteristics and mucin conformation) and b) determine the effect of non-mucin components present in the secretions, such as serum proteins (especially albumin, lysozyme, IgG, etc.), and polycations [Ca2+, polyamines (putrescine, spermidine and spermine) and low molecular weight basic proteins(s)] on the molecular aggregation and viscoelastic properties of the mucins. For these studies, the native and reduced mucin and non-mucin components will be purified from tracheobronchial secretions collected from a) CF patients; b) age and sex matched normal controls including normal siblings of CF patients and c) age and sex matched patients with bronchitis and asthma, using protocols established in this laboratory. Biochemical characterization of purified components will include: determination of carbohydrate, sulfate, amino acid composition, disulfide bond content, relative charge and molecular weight of the components. For biophysical characterization of the purified components of CF and control secretions, we will determine hydrophobic binding sites using fluorescence probe technique and molecular aggregation of mucins and other components using highly sensitive and versatile fluorescence polarization and light scattering techniques. Light scattering will be used to determine molecular weight of mucins, and of mucin aggregates as well as for determining conformation of mucin molecules (i.e. from radius of gyration determination). The viscoelastic properties will be determined using a magnetic microrheometer. These studies will aid in the understanding of underlying mechanism(s) responsible for abnormal viscoelastic properties of the CF secretions. Also, knowledge from studies will facilitate the development of a rational approach to the treatment of chronic lung disease in CF which ultimately must require an ability to control the viscoelastic properties, rate of secretion and elimination of the secretions.